In between munching on the snack, customers also breathe out cold air through their mouths and nostrils. Naturally, it is gaining traction on social media platforms such as Instagram and SnapChat, with customers posting photos and videos of the dessert.

Liquid nitrogen vaporises when exposed to air.

Over the past year, at least four Dragon's Breath vendors have been making their rounds at pop-up events. They include Abracowdabra, which sets up pop-up stalls regularly, and Coyoro, a dessert kiosk with locations in Bugis Street and at East Village mall in Upper Changi Road.

To put together a Dragon's Breath dessert, liquid nitrogen is dispensed from vacuum-insulated tanks that can be bought from nitrogen-tank suppliers, and used to flash-freeze a mixing bowl of snacks in under a minute.

Where to buy Dragon's Breath

ABRACOWDABRA

What: This pop-up shop adapts its menu to food trends. After selling cookie-dough desserts last year, it has morphed into a Dragon's Breath stall over the past three months. Each serving of Nitrogen Pop ($7) is loaded with banana-flavoured corn crackers that are double-dipped in liquid nitrogen so that the smoky effect lasts for up to a minute.

Where: Roving locations. It is at Wanderlust Market, a travel fair that is on until today, at Level 1 Marina Bay Sands Expo and Convention Centre, Halls A and B, 10 Bayfront Avenue, from 11am to 9.30pm.

What: It sells three types of Dragon's Breath desserts. The Original ($6) has corn crackers in grilled corn, milk, cheese and chocolate flavours; the Didi Ball ($6.50) comes with colourful cereal pops and a choice of strawberry and Nutella sauce; and Sweet Kiss ($7), which has meringue cookies.

What: After its popular maiden appearance at the Chinese New Year Bazaar in Temple Street, the pop-up stall will be at sustainable light art festival, i Light Marina Bay, from March 3 to 27. Its Dragon's Breath dessert ($8 a cup) is filled with bite-sized meringue cookies in five flavours, including mango, strawberry and chocolate.

1. Vendors advise consumers to avoid ingesting any droplets of liquid nitrogen on the cookies and crackers or at the bottom of the cup.

2. Ensure the liquid nitrogen has evaporated completely before consuming the snack.

3. Do not touch the frosty bites with your fingers. Use a skewer instead. Wave the snack in the air a few times or blow on it for a few seconds to reduce the coldness before eating.

4. Avoid resting the snack on your tongue or at the sides of your mouth. Bite into the snack immediately.

Dragon's Breath started appearing in night markets in the Philippines and South Korea two years ago. It then became a social media sensation after Chocolate Chair, a dessert shop in Los Angeles in the United States, started selling it last year.

Businesses here have been quick to offer it. The vendors have either watched online videos of the Dragon's Breath dessert or tried it overseas.

Ms Evelyn Wang, 21, co-owner of Abracowdabra, says Dragon's Breath is "the most Instagram-able street food in the world right now".

To prolong the smoky effect for up to a minute, she double-dips banana-flavoured crackers imported from South Korea in liquid nitrogen.

She says: "While the dessert doesn't have much flavour, most diners are after taking photos of the dessert and playing with their cold breath."

She sells 300 to 500 cups a day at pop-up events. Another vendor, Tio Smoke, has seen its sales surge since it started in March last year, with about 500 cups sold over a typical weekend event, thanks to viral online videos of Dragon's Breath.

However, its co-owners Derek Neo, 30, and Cai Xi Min, 25, observe that sales have dipped slightly with more competition from other Dragon's Breath vendors, since the middle of last year. They have also started catering to corporate events.

Ms Cai says: "It is a cool snack to have in a tropical country and more people can experience interesting desserts with liquid nitrogen that used to be exclusive to fine-dining restaurants."

Liquid nitrogen has long been used as a freezing agent to make ice cream in shops and restaurants, and it is also used in cocktails. Although consuming food that has been prepared with liquid nitrogen is harmless, the cryogenic liquid can cause frostbite or cold burns in the mouth if it is not consumed properly.

Ms Petrina Lim, Food & Beverage Technology domain lead at Temasek Polytechnic's School of Applied Science, says people should tuck in only when all the liquid nitrogen in the food has evaporated and there is no trace of the liquid left.

She says: "Ingesting even a few drops of liquid nitrogen would freeze the cells that it comes in contact with in a person's mouth, oesophagus and stomach. If liquid nitrogen boils off and evaporates into a gas in the stomach, it can lead to stomach perforation."

Five years ago, a woman had to undergo surgery to remove her stomach after drinking a liquid nitrogen cocktail in a bar in the United Kingdom.

To guard against these risks, Dragon's Breath vendors are taking precautions such as draining the snacks of liquid nitrogen before serving them and advising customers on proper ways to consume them.

Ms Cai of Tio Smoke says: "Eating Dragon's Breath is like popping an ice cube into your mouth. People with a low tolerance of coldness will feel discomfort." She adds that she has received at least one complaint of discomfort at each public event where she has set up her stall.

At Coyoro, which has seen its sales of Dragon's Breath desserts surge by 50 per cent over the past six months, a customer suffered from cold burns last year after a biscuit got stuck to the side of her gums.

That prompted the shop to refresh its training for staff on handling liquid nitrogen safely and giving customers instructions on how to eat Dragon's Breath. The shops also have posters warning about the risks of consuming liquid nitrogen.

A spokesman says: "Though there hasn't been any other cold burn incidents since, we have received feedback from customers that Dragon's Breath is too cold for them."

When contacted, the Consumers Association of Singapore says it has not received any complaints about Dragon's Breath in the past year.

Customers like the Dragon's Breath for the novelty of blowing out smoke, but most of them are not aware of the risks of consuming liquid nitrogen.

Ms Carin Lee, 25, a tourist from Malaysia, says: "I didn't think about the dangers of eating it. I am more interested in coming up with creative ways to take photos of this refreshing dessert."

Immigration officer Khairul Anuar, 27, who has tried Dragon's Breath twice, says: "It is fun to play with the smoke and take photos of this dessert, but I wouldn't recommend it for those with sensitive teeth, as biting into it can get rather uncomfortable."

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